1. Field of the Invention
The present invention relates to a device for counting printed products of an imbricated stream of printed products. The device includes a first measuring unit for detecting a printed product edge directed transversely of the conveying direction of the imbricated stream, and an evaluating unit which receives signals of the first measuring unit for counting the printed products.
2. Description of the Related Art
A device of the above-identified type is known in the art from U.S. Pat. No. 4,384,195. This device makes it possible to count, for example, newspapers which are conveyed in the imbricated stream prior to being shipped. For this purpose, a measuring unit is provided which includes a laser, wherein the laser directs light obliquely toward the imbricated stream. The light ray is reflected at each leading edge toward a receiver which sends appropriate signals to an evaluating unit. Between two adjacent edges, the light is reflected at the upper side of the respective printed product in such a way that the light does not reach the aforementioned receiver. Consequently, the measuring unit counts each leading edge of the respective printed products or newspapers.
In this device described above, there is the difficulty that a minimum spacing between edges of the printed products must exist in order to achieve an accurate counting result. Two printed sheets which are placed one on top of the other and printed sheets, whose spacing between the edges thereof is very small, are counted by this device as a single printed product. Accordingly, if the imbricated stream of printed products is irregular, the counting result of this device is incorrect. This means that orders can be only insufficiently monitored with respect to the number of products counted. An inaccurate counting result has the disadvantage that it may lead to overproduction or underproduction and to additional costs.
EP 1 201 582 A1 discloses a device for controlling sheets. However, in this device, the printed products are not counted, but defective sheets are detected. For determining such defective sheets, a device is provided with a capacitive sensor and at least one ultrasonic sensor. Using an output signal of an optical measuring unit, it is decided whether the sheets are controlled by means of the optical measurement unit or the capacitive measuring unit. This device makes possible a control of thin sheets as well as of thicker sheets.
EP 1 403 202 A1 discloses a method of operating a sensor for detecting sheets in a machine which processes sheets. In this method, the object is to accurately and securely distinguish between single sheets and multiple sheets with different stacking heights in sheet-processing machines. For this purpose, two different sensors are provided. Both sensors each detect the stacking height of the sheets. This method is also not suitable for counting products.